The photoautotrophic production of organic nitrogenous compounds is crucial to plant metabolism, growth, and development. Protein and amino acid contents of harvested plant materials are of great agronomic importance in many crop species. Light-driven nitrogen (N) assimilation in leaves has evolved to operate alongside and integrate with photosynthesis and respiration. The production of reduced carbon (C) in photosynthesis and its reoxidation in respiration are necessary to produce both the energy and C skeletons required for the incorporation of inorganic N into amino acids. Conversely, N assimilation is required to sustain the output of organic C and N. This network is further complicated by the concomitant operation of photorespiratory metabolism. Both the rate of N assimilation and the coordination of C and N assimilation are under multifactorial control by a repertoire of signals, which provide information on C and N status. There is a need for compositions and methods that can increase nitrogen content in plants under varying nitrogen conditions.